The nuclei in the brainstem which are the source of bulbospinal noradrenergic fibers are the locus coeruleus, A1, and A2. Their effect on spinal sensory transmission will be assessed by determining changes in single dorsal horn cell responses to cutaneous innocuous and noxious stimuli which result from electrical stimulation of these nuclei. The dependence of these effects on noradrenalin release will be evaluated by treating some of the experimental animals (cats) with the catecholamine neurotoxin 6-hydroxydopamine or the dopamine-Beta-hydroxylase inhibitor, fusaric acid. From prior experiments there is evidence that the spinal inhibitory effects of serotonin release may depend, in part, on functioning noradrenalin spinal terminals. This question will be approached by determining the effects of noradrenalin depletion with 6-hydroxydopamine and fusaric acid on the inhibition of dorsal horn cell responses caused by stimulation of the raphe nuclei.